In a wireless communication system such as 3GPP LTE, an LTE multimedia broadcast/multicast service (MBMS) is defined to efficiently provide broadcast and multicast services. The LTE MBMS applies a radio interface for transmitting broadcast and multicast data in a structure in which multiple cells operate like a single synchronized frequency network, i.e. in an MBSFN subframe. Meanwhile, MBSFN data is transmitted in correspondence to a physical multicast channel (PMCH) in terms of a physical layer. The PMCH recognizes an effective channel of a form in which channels of multiple cells are combined. Accordingly, an additional MBSFN reference signal (RS) for estimating the effective channel is transmitted through the PMCH.
In this case, presence of the PMCH and a PDSCH in the frequency domain in a specific subframe burdens a user equipment (UE) with simultaneous estimation of a cell-specific RS (CRS) based channel and an MBSFN RS based channel. To solve such a problem, the LTE system restricts transmission of the PDSCH in a subframe in which the PMCH is transmitted, referred to as an MBSFN subframe. Hence, the MBSFN subframe includes a downlink control region in a first or second OFDM symbol and the other region, i.e. the PMCH. While CRSs are transmitted in the control region, no CRSs are transmitted in the PMCH.
MBSFM subframes are semi-statically allocated according to a system information block (SIB) type 2 which is system information transmitted from higher layers. The system information may be updated at intervals of about twice or three times per hour. Accordingly, a transmission pattern of the MBSFM subframes may continue for a considerable time period. However, data for the MBMS is not always transmitted and partial resources among the allocated MBSFN subframes may not be used for the MBMS.
In LTE-A, a method for utilizing unused MBSFN subframes has been discussed and a method for transmitting unicast data for LTE-A UEs through the MBSFM subframe is proposed in consideration of the fact that legacy LTE UEs cannot expect that the unicast data will be transmitted in the MBSFM subframe.